Devices which employ moving parts are generally driven by motors or other electro-mechanical, hydraulic, or pneumatic mechanisms. Even in the best of conditions where all of the elements of the system are balanced, there is a tendency for moving parts to generate vibrational forces. In many contexts, these vibrational forces are undesirable, but do not significantly adversely affect the performance of the apparatus.
Another problem is mechanical shock which may be transmitted to an apparatus by acts as innocent as bumping into a table. An assortment of rubber feet and grommets have typically been placed underneath electronic devices such as computers in order to create a non-skid grip and to attempt to insulate the apparatus from the effects of mechanical shock or vibration. Rubber feet are typically affixed to the bottom of a chassis or board and it is placed on a table or other surface. The entire weight of the apparatus rests on the feet. Typically rubber feet do not provide a substantial amount of shock resistance or vibration dampening.
This approach is shown in Yagi, U.S. Pat. No. 5,079,655. A similar approach, the use of a rubber grommet, is shown in Krum, U.S. Pat. No. 5,035,396.
Grommets have been used in a variety of capacities, both to insulate and protect wire harnesses, and the like. as well as to dampen vibration. A typical grommet is formed of rubber or other playable material and has a slot in the side of the grommet. To attach a grommet to a circuit board or metal chassis, a hole is formed in the circuit board or chassis. The grommet is then deformed into the hole and the slot in the grommet positioned to match the circuit board or chassis. Wires may then be fed through the grommet, protecting them from the abrasive characteristics of a metal chassis, or circuit board. In certain applications, screws are fed through the center of a grommet to attach the chassis to a mounting surface. The screws are typically tightened as much as is practically possible by the installer. The primary use of the grommet in this fashion is to mount the chassis or circuit board to another surface and electrically insulate or isolate the chassis or circuit board. In applications where a shock mount or vibration mount is more desired, a large washer is typically placed over the grommet and a machine screw is fed through the hole in the washer and the grommet and tightened against the mounting platform.
This mounting technique does not provide for vibrational dampening or shock mounting characteristics that are widely repeatable from unit to unit as the position and size of the washer, as the strength of the assembler will determine the compression of the grommet, and thus the dampening characteristics of the assembly.
U.S. Pat. No. 4,901,014, issued to Rigger, employs two O-rings located around a hollow shaft of a rotational signal generator to compensate for misalignments of the rotatable component part. The O-rings are tightly sandwiched between the central hollow shaft, and the surrounding generator carrier or frame. Rigger does not seek to measure or equalize forces amongst a variety of pressure points, nor to actively reduce vibration of the assembly, but merely to compensate for misalignment of a signal generator component.
Floppy disk drives have been around for a number of years, and originally had a track width of approximately 121/2 thousandths of an inch. These disk drives originally had a capacity of 360 kilobytes of data, stored on both sides of a 51/4" floppy. Vibrational effects were not particularly devastating given the width of the track and the density of data storage. These disk drives had a track density of 48 tracks per inch and a track to track spacing of approximately 121/2 thousandths of an inch. Additionally, the data transfer frequency was relatively slow, alternating between 125 khz and 250 khz, depending on the data encryption scheme being employed.
As floppy disk drives have improved, the track density has increased to 96 tracks per inch, and beyond, and the data transfer rate has effectively doubled, employing data transfer frequencies of 250 kHz or 500 kHz, depending on the data encryption scheme. In a similar manner, Winchester-type disk drives have seen a dramatic increase in the track density, 500-1,000 tracks per inch and possibly greater track densities presently being employed in a number of applications. This results in a extremely narrow track width and narrow track-to-track spacing. In addition, the data transfer rate has increased dramatically and data transfer rates of 5 MHz are not uncommon.
The effect of the narrow track widths and the high data transfer rate has resulted in the Winchester disk drive being susceptible to data transfer errors due to variations in motor speed operation, or movement of the heads with respect to the track on the storage media. This has resulted in higher precision motors being employed, as well as more precise head location schemes which typically include track positioning schemes which are highly accurate, and may be closed loop servo systems.
Additional problems are created by moving or shaking a disk drive such as a Winchester type disk drive during operation. The motor speed may be varied in an undesirable manner, or the heads may be momentarily displaced from the desired track.
One solution which has been employed in some Winchester-type disk drive products has been a bonded rubber design in which a rubber gasket or bracket is bonded to the surface of the disk drive surrounding a mounting hole, or located between mating surfaces of the disk drive assembly and mounting platform assembly. This type of design tends to be expensive to implement in each of the mounting locations. In addition, the bonded rubber design does not allow the flexibility of rapid replacement of the vibration reduction mechanism, that being the bonded rubber itself. Further, the response characteristics of the bonded rubber design is determined when the rubber is affixed to the mounting surface, and cannot be varied later except by destroying or removing the rubber material itself.